Golf ball cover compositions

ABSTRACT

The present invention is directed to improved cover compositions for golf ball construction and the resulting golf balls produced utilizing the improved cover compositions. The novel golf ball cover compositions of the invention comprise a blend of hard ionomeric resins, preferably acrylic acid based ionomers, and recently developed acrylic acid based soft ionomers. When the cover compositions of the invention are utilized to manufacture golf balls, the golf balls produced thereby, exhibit properties of improved distance without sacrificing playability and/or durability when compared to known hard-soft ionomer blends.

This is a continuation of application Ser. No. 07/860,455 filed Mar. 30,1992 now abandoned.

This is a continuation of application Ser. No. 08/218,699 filed Mar. 28,1994 now abandoned.

This is a continuation-in-part application of U.S. Ser. No. 07/559,177,filed on Jul. 27, 1990 now U.S. Pat. No. 5,120,791 which is incorporatedby reference herein.

BACKGROUND OF THE INVENTION

The present invention concerns improved hard-soft ionomeric resinmixtures (or blends) which are particularly well suited for theformulation of the cover composition of a golf ball.

More specifically, the present invention relates to novel golf ballcover compositions comprising blends of hard ionomer resins withrecently developed soft ionomer resins made from acrylic acid basedpolymers. The new compositions of the present invention, when utilizedfor golf ball construction, particularly the construction of two piecegolf balls, produce golf balls exhibiting enhanced travel distancewithout sacrificing the properties of playability and/or durability.

Ionomeric resins are polymers containing interchain ionic bonding. As aresult of their toughness, durability, and flight characteristics,various ionomeric resins sold by E.I. DuPont deNemours & Company underthe trademark “Surlyn®” and more recently, by the Exxon Corporation (seeU.S. Pat. No. 4,911,451) under the trademarks “Escor® and the tradename“Iotek”, have become the materials of choice for the construction ofgolf ball covers over the traditional “balata” (trans polyisoprene,natural or synthetic) rubbers. The softer balata covers, althoughexhibiting enhanced playability properties, lack the durabilitynecessary for repetitive play.

Ionomeric resins are generally ionic copolymers of an olefin such asethylene and a metal salt of an unsaturated carboxylic acid, such asacrylic acid, methacrylic acid, or maleic acid. Metal ions, such assodium or zinc, are used to neutralize some portion of the acidic groupsin the copolymer resulting in a thermoplastic elastomer exhibitingenhanced properties, i.e. improved durability, etc., for golf ball coverconstruction over balata. However, the advantages gained in increaseddurability have been offset to some degree by the decreases produced inplayability. This is because although the ionomeric resins are verydurable, they tend to be very hard when utilized for golf ball coverconstruction, and thus lack the degree of softness required to impartthe spin necessary to control the ball in flight.

As a result, while there are currently more than fifty commercial gradesof ionomers available from DuPont and Exxon with a wide range ofproperties which vary according to the type and amount of metal cations,molecular weight, composition of the base resin (i.e. relative contentof ethylene and methacrylic and/or acrylic acid groups) and additiveingredients such as reinforcements, etc., a great deal of researchcontinues in order to develop golf ball cover compositions exhibitingnot only the improved impact resistance and carrying distance propertiesproduced by the “hard” ionomeric resins, but also the playability (i.e.“spin”) characteristics previously associated with the “soft” balatacovers, properties which are still desired by the more skilled golfer.

In various attempts to produce such an ideal golf ball, the golfingindustry has blended the hard ionomeric resins with a number of softerpolymeric materials, such as softer polyurethanes. However, the blendsof the hard ionomer resins with the softer polymeric materials havegenerally been dissatisfactory in that these balls exhibit numerousprocessing problems. In addition, the balls produced by such acombination are usually short on distance.

In addition, various “hard-soft ionomeric blends”, i.e. mixtures ofionomer resins which are significantly different in hardness and/orflexural modulus, have been attempted. However, until the development ofthe specific blend combination set forth in U.S. Pat. No. 4,884,814,these balls were not particularly commercially viable. In this regard,although the balls produced using the hard-soft ionomer blends exhibitedenhanced playability characteristics, they lacked the durability neededfor continuous play.

U.S. Pat. No. 4,884,814, the present inventors previous patent, isdirected to the finding that if various “hard” Surlyn® methacrylic acidbased ionomer resins (i.e. those Surlyn® resins having a hardness ofabout 60 to 66 on the Shore D scale as measured in accordance with ASTMmethod D-2240) were blended with a number of specific “soft” Surlyn®methacrylic acid based ionomer resins (i.e. those Surlyn® resins havinga hardness from about 25 to 40 as measured on the Shore D scale) that agolf ball cover composition could be produced that is not only softerthan the prior art hard ionomer covers but also exhibits a sufficientdegree of durability for repetitive play.

As a result, a golf ball covered in accordance with the “hard-soft”methylacrylic acid based ionomer blends of the '814 patent, exhibitsproperties of enhanced playability (i.e. softness and spin) anddurability. However, notwithstanding the above, some sacrifice incarrying distance is also exhibited in comparison with the ballsproduced utilizing the hard Surlyn® resins.

The present invention is directed to new golf ball cover compositionswhich exhibit properties of enhanced carrying distance (i.e. possesshigher coefficient of restitution values) than the hard-soft ionomerblends set forth in U.S. Pat. No. 4,884,814, without sacrificingcharacteristics such as playability (i.e. softness and spin) and/ordurability. It has been found that these properties can be producedusing improved hard-soft ionomer blends containing recently developedacrylic acid based soft ionomer resins.

SUMMARY OF THE INVENTION

The present invention is directed to improved cover compositions forgolf ball construction and the resulting golf balls produced utilizingthe improved cover compositions. The novel golf ball cover compositionsof the invention comprise a blend of hard ionomeric resins, preferablyacrylic acid based ionomers, and recently developed acrylic acid basedsoft ionomers. When the cover compositions of the invention are utilizedto manufacture golf balls, the golf balls produced thereby, exhibitproperties of improved distance without sacrificing playability and/ordurability when compared to known hard-soft ionomer blends.

Two of the principal properties involved in the performance of golfballs are resilience and hardness. Resilience is determined by thecoefficient of restitution (C.O.R.), the constant “e”, which is theratio of the relative velocity of two elastic spheres after directimpact to that before impact. As a result, the coefficient ofrestitution (i.e. “e”) can vary from zero to one, with one beingequivalent to an elastic collision and zero being equivalent to aninelastic collision.

Resilience (C.O.R.), along with additional factors such as clubheadspeed, angle of trajectory, and ball configuration (i.e. dimplepattern), generally determines the distance a ball will travel when hit.Since clubhead speed and the angle of trajectory are not factors easilycontrollable, particularly by golf ball manufacturers, the factors ofconcern among manufacturers are the coefficient of restitution (C.O.R.)and the surface configuration of the ball.

The coefficient of restitution (C.O.R.) in solid core balls is afunction of the composition of the molded core and of the cover.

In balls containing a wound core (i.e. balls comprising a liquid orsolid center, elastic windings, and a cover), the coefficient ofrestitution is a function of not only the composition of the center andcover, but also the composition and tension of the elastomeric windings.Although both the core and the cover contribute to the coefficient ofrestitution, the present invention is directed solely to the coefficientof restitution which is affected by the cover composition.

In this regard, the coefficient of restitution of a golf ball isgenerally measured by propelling a ball at a given speed against a hardsurface and measuring the ball's incoming and outgoing velocityelectronically. As mentioned above, the coefficient of restitution isthe ratio of the outgoing velocity to incoming velocity. The coefficientof restitution must be carefully controlled in all commercial golf ballsin order for the ball to be within the specifications regulated by theUnited States Golf Association (U.S.G.A.). Along this line, the U.S.G.A.standards indicate that a “regulation” ball cannot have an initialvelocity (i.e. the speed off the club) exceeding 255 feet per second.Since the coefficient of restitution of a ball is related to the ball'sinitial velocity, it is highly desirable to produce a ball having asufficiently high coefficient of restitution to closely approach theU.S.G.A. limit on initial velocity, while having an ample degree ofsoftness (i.e. hardness) to produce enhanced playability (i.e. spin,etc.).

The hardness of the ball is the second principal property involved inthe performance of a golf ball. The hardness of the ball can affect theplayability of the ball on striking and the sound or “click” produced.Hardness is determined as the deformation (i.e. compression) of the ballunder various load conditions applied across the ball's diameter (i.e.the lower the compression value, the harder the material). As indicatedin U.S. Pat. No. 4,674,751, “softer” covers permit the accomplishedgolfer to impart proper spin. This is because the softer covers deformon impact significantly more than balls having “harder” ionomeric resincovers. As a result, this allows the better player to impart fade, draw,or backspin to the ball thereby enhancing playability. Such propertiescan be determined by various “spin rate tests”, such as the “nine-iron”spin rate test set forth below.

Accordingly, the present invention is directed to new hard- soft ionomerblends which produce, upon molding around solid or wound cores toformulate a cover composition, golf balls exhibiting enhanced distance(i.e. resilience) without adversely affecting, and in many instances,improving the ball's playability (i.e. hardness/softness) and/ordurability (i.e. impact resistance, etc.) characteristics.

These and other objects and features of the invention will be apparentfrom the following description and from the claims.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to improved cover compositions for golfball construction. More particularly, the present invention is directedto improved blends of hard and soft ionomers, which, when utilized toformulate the cover stock of golf balls, produce golf balls havingenhanced properties, including longer distance with similar or improvedplayability properties (i.e. higher Riehle compression, lower Shorehardness values, etc.), when compared to golf balls produced by thehard-soft ionomer blends of the prior art. The improved propertiesproduced by the hard-soft ionomer blends of the present invention aredue to the use of recently developed acrylic acid based soft ionomers,which produce cover compositions having lower flexural modulus andhardness (i.e. enhanced softness) and improved coefficients ofrestitution when incorporated with the hard ionomer resins indicatedbelow.

The hard (high modulus) ionomers suitable for use in the presentinvention include those ionomers having a hardness greater than 50 onthe Shore D scale as measured in accordance with ASTM method D-2240, anda flexural modulus from about 15,000 to about 70,000 psi as measured inaccordance with ASTM method D-790.

The hard ionomer resins utilized to produce the cover compositions areionic copolymers which are the sodium, zinc, magnesium or lithium saltsof the reaction product of an olefin having from 2 to 8 carbon atoms andan unsaturated monocarboxylic acid having from 3 to 8 carbon atoms. Thecarboxylic acid groups of the copolymer may be totally or partially(i.e. approximately 15-75 percent) neutralized.

Preferably, the hard ionomeric resins are copolymers of ethylene andeither acrylic and/or methacrylic acid, with copolymers of ethylene andacrylic acid the most preferred. In addition, two or more types of hardionomeric resins may be blended into the cover compositions in order toproduce the desired properties of the resulting golf balls.

Although the scope of the patent embraces all known hard ionomericresins falling within the parameters set forth above, only a relativelylimited number of these hard ionomeric resins are commerciallyavailable. In this regard, the hard ionomeric resins sold by E.I. DuPontde Nemours Company under the trademark “Surlyn®”, and the hard ionomerresins sold by Exxon Corporation under either the trademark “Escor®” orthe tradename “Iotek” are examples of commercially available hardionomeric resins which may be utilized in the present invention in theparticular combinations described in detail below.

The hard ionomeric resins introduced under the designation “Escor®” andnow sold under the new designation “Iotek”, are somewhat similar to thehard ionomeric resins sold under the “Surlyn®” trademark. However, sincethe “Iotek” ionomeric resins are sodium or zinc salts of poly(ethyleneacrylic acid) and the “Surlyn” resins are zinc or sodium salts ofpoly(ethylene methacrylic acid) some distinct differences in propertiesexist. As more specifically indicated in the data set forth below, thehard Iotek resins (i.e. the acrylic acid based hard ionomer resins) arethe more preferred hard resins for use in the present invention. Inaddition, various blends of “Iotek” and “Surlyn” hard ionomeric resins,as well as other available ionomeric resins, may be utilized in thepresent invention.

Examples of commercially available hard ionomeric resins which may beutilized in the present invention include the hard sodium ioniccopolymer sold under the trademark “Surlyn 8940” and the hard zinc ioniccopolymer sold under the trademark “Surlyn 9910”. Surlyn 8940 is acopolymer of ethylene with methacrylic acid with about 15 weight percentacid which is about 29% neutralized with sodium ions. This resin has anaverage melt flow index of about 2.8. Surlyn 9910 is a copolymer ofethylene and methacrylic acid with about 15 weight percent acid which isabout 58% neutralized with zinc ions. The average melt flow index ofSurlyn 9910 is about 0.7. The typical properties of Surlyn 9910 and 8940are set forth below in Table 1. TABLE 1

TABLE 1 Typical Properties of Commercially Available Hard Surlyn ®Resins Suitable for Use in the Present Invention ASTM D 8940 9910 89208528 9970 9730 Cation Type Sodium Zinc Sodium Sodium Zinc Zinc Melt flowindex, D-1238 2.8 0.7 0.9 1.3 14.0 1.6 gms/10 min. Specific Gravity,D-792 0.95 0.97 0.95 0.94 0.95 0.95 g/cm³ Hardness, Shore D D-2240 66 6466 60 62 63 Tensile Strength, D-638 (4.8) (3.6) (5.4) (4.2) (3.2) (4.1)(kpsi), MPa 33.1 24.8 37.2 29.0 22.0 28.0 Elongation, % D-638 470 290350 450 460 460 Flexural Modulus, D-790 (51) (48) (55) (32) (28) (30)(kpsi) MPa 350 330 380 220 190 210 Tensile Impact (23° C.) D-18225 10201020 865 1160 760 1240 KJ/m₂ (ft.-lbs./in²) (485) (485) (410) (550)(360) (590) Vicat Temperature, ° C. D-1525 63 62 58 73 61 73

In addition, examples of the more pertinent acrylic acid based hardionomer resins suitable for use in the present invention sold under the“Iotek” tradename by the Exxon Corporation include “Iotek 4000”(formerly “Escor 4000”), “Iotek 4010”, “Iotek 8000” (formerly Escor900), “Iotek 8020”, and “Iotek 8030”. The typical properties of theIotek hard ionomers are set forth below in Table 2.

TABLE 2 Typical Properties of Iotek Ionomers ASTM Method Units 4000 40108000 8020 8030 Resin Properties Cation type zinc zinc sodium sodiumsodium Melt index D-1238 g/10 min. 2.5 1.5 0.8 1.6 2.8 Density D-1505kg/m³ 963 963 954 960 960 Melting Point D-3417 ° C. 90 90 90 87.5 87.5Crystallization Point D-3417 ° C. 62 64 56 53 55 Vicat Softening PointD-1525 ° C. 62 63 61 64 67 % Weight Acrylic Acid 16 11 % of Acid Groups30 40 cation neutralized Plaque Properties (3 mm thick, compressionmolded) Tensile at break D-638 MPa 24 26 36 31.5 28 Yield point D-638MPa none none 21 21 23 Elongation at break D-638 % 395 420 350 410 3951% Secant modulus D-638 MPa 160 160 300 350 390 Shore Hardness D D-2240— 55 55 61 58 59 Film Properties (50 micron film 2.2:1 Blow-up ratio)Tensile at Break MD D-882 MPa 41 39 42 52 47.4 TD D-882 MPa 37 38 38 3840.5 Yield point MD D-882 MPa 15 17 17 23 21.6 TD D-882 MPa 14 15 15 2120.7 Elongation at Break MD D-882 % 310 270 260 295 305 TD D-882 % 360340 280 340 345 1% Secant modulus MD D-882 MPa 210 215 390 380 380 TDD-882 MPa 200 225 380 350 345 Dart Drop Impact D-1709 g/micron 12.4 12.520.3

The critical soft (low modulus) ionomers utilized to formulate theblends of the present invention are acrylic acid based soft ionomers.These soft ionomers may be generally characterized as comprised ofsodium or zinc salts of a terpolymer of an olefin having from about 2 to8 carbon atoms, acrylic acid, and an unsaturated monomer of the acrylateester class having from 1 to 22 carbon atoms. Preferably, the softionomer is a zinc based ionomer made from an acrylic acid base polymerand an unsaturated monomer of the acrylate ester class. The soft (lowmodulus) ionomers have a hardness from about 20 to about 40 (preferablyfrom about 30 to about 40) as measured on the Shore D scale and aflexural modulus from about 2,000 to about 10,000 psi (preferably fromabout 3,000 to 7,000 psi) as measured in accordance with ASTM methodD-790.

More particularly, the present inventors have discovered that if the newacrylic acid based experimental soft ionomers recently developed by theExxon Corporation for the Spalding Sports Worldwide, a division ofSpalding & Evenflo Companies, Inc., Tampa, Fla., are utilized with thespecific hard ionomers described above, in the combinations more clearlydefined below and demonstrated in the Examples, not only areimprovements in processability and clarity seen, but also the overallcombinations, when utilized for golf ball construction, produce golfballs having higher coefficient of restitution values (i.e. longerdistance) at equal or softer hardness than golf balls produced by knownhard-soft ionomer blends, including the hard-soft ionomer blendsutilized to produce Spalding's current Tour Editions® ball.

In this regard, the inventors have found that when the newethylene-acrylic acid based soft ionomer resins recently developed bythe Exxon Corporation under the designations “Iotek 7520” (referredexperimentally by differences in neutralization and melt indexes as LDX195, LDX 196, LDX 218 and LDX 219) and “Iotek 7510” are combined withthe known hard ionomers indicated above, the combination produces higherC.O.R.s at equal or softer hardness, higher melt flow (which correspondsto improved, more efficient molding, i.e. fewer rejects), as well assignificant cost savings versus balls produced by known hard-softionomer blends due to lower overall raw materials cost and improvedyields.

While the exact chemical composition of the resins to be sold by Exxonunder the designation Iotek 7520 is considered by Exxon to beconfidential and proprietary information, Exxon's Experimental ProductData sheet lists the following physical properties of this ethyleneacrylic acid zinc ionomer developed by Exxon:

TABLE 3 Property ASTM Method Units Typical Value Physical Properties ofIotek 7520 Melt Index D-1238 g/10 min. 2 Density D-1505 kg/m³ 0.962Cation Zinc Melting Point D-3417 ° C. 66 Crystallization D-3417 ° C. 49Point Vicat Softening D-1525 ° C. 42 Point Plaque Properties (2 mm thickCompression Molded Plaques) Tensile at Break D-638 MPa 10 Yield PointD-638 MPa None Elongation at Break D-638 % 760 1% Secant Modulus D-638MPa 22 Shore D Hardness D-2240 32 Flexural Modulus D-790 MPa 26 ZwickRebond ISO 4862 % 52 De Mattia Flex D-430 Cycles >5000 Resistance

In addition, test data collected by the inventors indicates that Iotek7520 resins have Shore D hardnesses of about 32-36 (per ASTM D-2240),melt flow indexes of 3±0.5 g/10 min (at 190° C. per ASTM D-1288), aflexural moduluses of about 2500-3500 psi (per ASTM D-790). Furthermore,testing by an independent testing laboratory by pyrolysis massspectrometry indicates that the Iotek 7520 resins are generally zincsalts of a terpolymer of ethylene, acrylic acid, and methyl acrylate.

Furthermore, the inventors have found that a newly developed grade of anacrylic acid based soft ionomer available from the Exxon Corporationunder the designation Iotek 7510, is also effective, when combined withthe hard ionomers indicated above in producing golf ball coversexhibiting higher C.O.R. values at equal or softer hardness than thoseproduced by known hard-soft ionomer blends. In this regard, Iotek 7510produces has the advantages (i.e. improved flow, higher C.O.R. valves atequal hardness, increased clarity, etc.) produced by the Iotek 7520resin when compared to the methacrylic acid base soft ionomers known inthe art (such as the Surlyn 8625 and the Surlyn 8629 combinationsdisclosed in U.S. Pat. No. 4,884,814).

In addition, Iotek 7510, when compared to Iotek 7520, produces slightlyhigher C.O.R. valves at equal softness/hardness due to the Iotek 7510'shigher hardness and neutralization. Similarly, Iotek 7510 producesbetter release properties (from the mold cavities) due to its slightlyhigher stiffness and lower flow rate than Iotek 7520. This is importantin production where the soft covered balls tend to have lower yieldscaused by sticking in the molds and subsequent punched pin marks fromthe knockouts.

According to Exxon, Iotek 7510 is of similar chemical composition asIotek 7520 (i.e. a zinc salt of a terpolymer of ethylene, acrylic acid,and methyl acrylate) but is more highly neutralized. Based upon FTIRanalysis, Iotek 7520 is estimated to be about 30-40 wt.-% neutralizedand Iotek 7510 is estimated to be about 40-60 wt.-% neutralized. Thetypical properties of Iotek 7510 in comparison of those of Iotek 7520are set forth below:

TABLE 4 Physical Properties of Iotek 7510 in Comparison to Iotek 7520IOTEK 7520 IOTEK 7510 MI, g/10 min 2.0 0.8 Density, g/cc 0.96 0.97Melting Point, ° F. 151 149 Vicat Softening Point, ° F. 108 109 FlexModulus, psi 3800 5300 Tensile Strength, psi 1450 1750 Elongation, % 760690 Hardness, Shore D 32 35

As mentioned above and more clearly indicated below in the Examples, therecently developed ethylene-acrylic acid based soft ionomers (i.e. theIotek 7520 and the Iotek 7510 resins) produce, when combined withvarious hard ionomers, particularly the Escor® hard ionomers, golf ballsexhibiting enhanced properties, including longer distance at similar orsofter hardness, over known hard-soft ionomer blends including those setforth in the U.S. Pat. No. 4,884,814 concerning related subject matter.Along this line, while the '814 patent is directed to various hard-softSurlyn® ionomer blends which are similar to those blends utilized toformulate Spalding's current Tour Edition® golf ball, the soft Surlynionomers (i.e. the Surlyn 8265 and 8269 resins) disclosed therein are ofthe poly(ethylene-methacrylic acid-butyl acrylate) type. The inventorshave now discovered that the use of soft ionomers containing acrylicacid (i.e. the Iotek 7520 and the Iotek 7510 resins), as opposed tomethacrylic acid (i.e. the Surlyn 8265 and the 8269 resins), produce amore desirable golf ball in terms of distance and hardness (softness)while maintaining durability when used in combination with various knownhard resins.

The superior golf balls of the present invention containing the improvedhard-soft ionomer blends can be generally produced from a central coreand an outer cover wherein the outer cover is made from a compositioncomprised of a blend of about 90 to about 10 percent of a hard ionomerof the type indicated above, and about 10 to about 90 percent of anacrylic acid based soft ionomer.

More preferably, it has been found that a golf ball exhibitingproperties of enhanced travel distance (i.e. higher C.O.R. values) withsimilar or improved playability (i.e. softness characteristics) withouta sacrifice in durability, can be produced from a core and a cover,wherein the cover is made from a composition comprised of about 70 to 30percent of a hard ionomer resin, and about 30 to about 70 percent of anacrylic acid based soft ionomer, depending on the degree of softnessdesired.

Superior results may be achieved when the hard ionomers utilized aresodium or zinc salts of poly(ethylene acrylic acid) such as those soldby Exxon under the Iotek designation, particularly Iotek 4000 and Iotek8000, and the soft ionomers utilized are the new acrylic acid based softionomers recently developed by Exxon under the designations Iotek 7520and Iotek 7510. The optimal ranges of hard to soft ionomers are fromabout 60 to about 40 percent hard ionomer and from about 40 to about 60percent soft ionomer.

Additional materials may also be added to the compositions of thepresent invention, including dyes (for example, Ultramarine Blue sold byWhitaker, Clark, and Daniels of South Plainsfield, N.J.) (see U.S. Pat.No. 4,679,795), pigments such as titanium dioxide, zinc oxide, bariumsulfate and zinc sulfate; UV absorbers; antioxidants; antistatic agents;and stabilizers. Moreover, the cover compositions of the presentinvention may also contain softening agents, such as plasticizers,processing aids, etc., and reinforcing materials such as glass fibersand inorganic fillers, as long as the desired properties produced by thegolf ball covers of the invention are not impaired.

The cover compositions of the present invention may be producedaccording to conventional melt blending procedures. Generally, the hardionomer resins are blended with the soft ionomeric resins in a Banburytype mixer, two-roll mill, or extruder prior to molding. The blendedcomposition is then formed into slabs and maintained in such a stateuntil molding is desired. If necessary, further additives such asinorganic fillers, antioxidants, stabilizers, and/or zinc oxide may beadded and uniformly mixed before initiation of the molding process.

The golf balls of the present invention can be produced by moldingprocesses currently well known in the golf ball art. Specifically, thegolf balls can be produced by injection molding or compression moldingthe novel cover compositions about wound or solid molded cores toproduce a golf ball having a diameter of about 1.680 inches and weighingabout 1.620 ounces. The standards for both the diameter and weight ofthe balls are established by the United States Golf Association(U.S.G.A.). Although both solid core and wound cores can be utilized inthe present invention, as a result their lower cost and superiorperformance, solid molded cores are preferred over wound cores.

Conventional solid cores are typically compression molded from a slug ofuncured or lightly cured elastomer composition comprising a high ciscontent polybutadiene and a metal salt of an α, βethylenicallyunsaturated carboxylic acid such as zinc mono or diacrylate ormethacrylate. To achieve higher coefficients of restitution in the core,the manufacturer may include a small amount of a metal oxide such aszinc oxide. In addition, larger amounts of metal oxide than are neededto achieve the desired coefficient may be included in order to increasethe core weight so that the finished ball more closely approaches theU.S.G.A. upper weight limit of 1.620 ounces. Other materials may be usedin the core composition including compatible rubbers or ionomers, andlow molecular weight fatty acids such as stearic acid. Free radicalinitiator catalysts such as peroxides are admixed with the corecomposition so that on the application of heat and pressure, a complexcuring or cross-linking reaction takes place.

The term “solid cores” as used herein refers not only to one piece coresbut also to those cores having a separate solid layer beneath the coverand above the core as in U.S. Pat. No. 4,431,193, and other multilayerand/or non-wound cores.

Wound cores are generally produced by winding a very large elasticthread around a solid or liquid filled balloon center. The elasticthread is wound around the center to produce a finished core of about1.4 to 1.6 inches in diameter, generally. Since the core material is notan integral part of the present invention, a detailed discussionconcerning the specific types of core materials which may be utilizedwith the cover compositions of the invention are not specifically setforth herein. In this regard, the cover compositions of the inventionmay be used in conjunction with any standard golf ball core.

As indicated, the golf balls of the present invention may be produced byforming covers consisting of the compositions of the invention aroundcores by conventional molding processes. For example, in compressionmolding, the cover composition is formed via injection at about 380° F.to about 450° F. into smooth surfaced hemispherical shells which arethen positioned around the core in a dimpled golf ball mold andsubjected to compression molding at 200-300° F. for 2-10 minutes,followed by cooling at 50-70° F. for 2-10 minutes, to fuse the shellstogether to form an unitary ball. In addition, the golf balls may beproduced by injection molding, wherein the cover composition is injecteddirectly around the core placed in the center of a golf ball mold for aperiod of time at a mold temperature of from 50° F. to about 100° F..After molding the golf balls produced may undergo various furtherprocessing steps such as buffing, painting, and marking.

The resulting golf balls produced from the novel hard-soft ionomericresin combinations of the present invention exhibit enhanced distanceand playability properties over the art without sacrificing durability.This is due to the use of acrylic acid based ionomers as the softionomer in the overall cover stock composition.

The present invention is further illustrated by the following examplesin which the parts of the specific ingredients are by weight. It is tobe understood that the present invention is not limited to the examples,and various changes and modifications may be made in the inventionwithout departing from the spirit and scope thereof.

EXAMPLES

By blending the ingredients set forth in the Tables below, a series ofcover formulations were produced. In the examples, cover formulationscontaining the acrylic acid based soft ionomers-hard ionomer blends ofthe present invention were compared with the hard-soft ionomer blends ofthe prior art including the hard-soft ionomer blend utilized to producethe current Tour Edition® ball (see Examples 3, 11 and 24) which is thesubject of U.S. Pat. No. 4,884,814.

In addition, the properties produced by the cover compositionsformulated with the acrylic acid based soft ionomer-hard ionomer blendsof the present invention were compared to the properties produced by thecover materials representative of the Tour Edition®, Tour Edition®100and the Top Flite® II balls currently being sold by Spalding & EvenfloCompanies, Inc., Tampa, Fla., as well as a wide variety of competitivegolf balls available in the market place. Although the specificformulations utilized to produce the Tour Edition® 100 and Top Flite®balls are proprietary, these formulations were utilized under the sameprocessing conditions as those set forth below in order to producecovered golf balls for comparison purposes.

Along this line, the current Tour Edition® ball is unique in that it isa two piece solid core, molded cover ball that meets the needs ofgolfers who demand superior control, historically obtained only withbalata covered wound balls. It offers superior playability at thesacrifice of coefficient of restitution, which relates directly todistance.

The Tour Edition® 100 ball has a slightly softer cover than the TourEdition® ball and utilizes a unique twin-dimple design. The TourEdition® 100 ball more closely meets the demands of the pro tour golferthan any other Spalding ball previously produced.

The Top Flite® ball is considered to be a “hard” Surlyn or Iotekionomeric resin ball. As a result of the ball's hardness, the Top Flite®ball is a difficult ball for golfers to control. Generally, the harderthe golf ball, the more difficult it is for a golfer to impart spin tothe ball, and hence, control the ball during flight. However, as aresult of its outstanding durability and maximum distance, the ball iswidely accepted by a large percentage of golfers.

The present invention is directed to various blends of hard ionomers andacrylic acid based soft ionomers, which, when utilized for golf ballcover construction, produce golf balls closely approaching the superiordistance properties exhibited by the current Top Flite® ball withoutsacrificing the playability characteristics of the current Tour Edition®ball.

The cover formulations set forth below in Tables 5, 6 and 7 wereinjection molded at 400° F. around identical solid type cores having afinished diameter of 1.545 inches to produce golf balls approximately1.680 inches in diameter having nominal cover thickness of 0.0675inches. The properties of Riehle compression, coefficient of restitution(C.O.R.), Shore Hardness, impact resistance, and spin rate for the coverformulation were determined. In Tables 5 and 6, Examples 3 and 11 areidentical, and Examples 19 and 22 are similar in composition (i.e.different neutralization and melt index grades of Iotek 7520 whereutilized). These Examples have been set forth for comparison purposes.The data for each example represents the average data for one dozenballs produced according to the desired manner. The properties weremeasured according to the following parameters:

Riehle compression is a measurement of the deformation of a golf ball ininches under a fixed static load of 225 pounds.

Coefficient of restitution (C.O.R.) was measured by firing the resultinggolf ball is an air cannon at a velocity of 125 feet per second againsta steel plate which is positioned 12 feet from the muzzle of the cannon.The rebound velocity was then measured. The rebound velocity was dividedby the forward velocity to give the coefficient of restitution.

Shore hardness was measured in accordance with ASTM Test 2240.

Cut resistance was measured in accordance with the following procedure:A golf ball is fired at 135 feet per second against the leading edge ofa pitching wedge, wherein the leading edge radius is {fraction (1/32)}inch, the loft angle is 51 degrees, the sole radius is 2.5 inches, andthe bounce angle is 7 degrees.

The cut resistance of the balls tested herein was evaluated on a scaleof 1-5. 5 represents a cut that extends completely through the cover tothe core; a 4 represents a cut that does not extend completely throughthe cover but that does break the surface; a 3 does not break thesurface of the cover but does leave a permanent dent; a 2 leaves only aslight crease which is permanent but not as severe as 3; and a 1represents virtually no visible indentation or damage of any sort.

The spin rate of the golf ball was measured by striking the resultinggolf balls with a pitching wedge or 9-iron wherein the club-head speedis about 80 feet per second and the ball is launched at an angle of 26to 34 degrees with an initial velocity of about 110-115 feet per second.The spin rate was measured by observing the rotation of the ball inflight using stop action Strobe photography.

Initial velocity is the velocity of a golf ball when struck at a hammerspeed of 143.8 feet per second in accordance with a test as prescribedby the U.S.G.A.

TABLE 5 Formulations 1 2 3 4 5 6 7 8 9 10 INGREDIENTS Surlyn 9910 438 —486 486 486 — — — — — Surlyn 8940 1370 — 108 108 108 — — — — — Surlyn8269 — — 832 — — — — — — — Surlyn 8265 — — 362 362 — — — — — — SurlynWhite MB¹ 193 — 193 193 193 — — — — — Escor 4000 (Iotek 4000) — 904 — —— 300 400 500 — — Escor 900 (Iotek 8000) — 904 — — — 300 400 500 8001000 Escor White MB² — 193 — — — 193 193 193 — — LDX-195 (Iotek 7520) —— — — — — — — 988 788 LDX-196 (Iotek 7520) — — — 832 1194 1188 988 788 —— PROPERTIES Shore C Hardness 93 95 85 82 79 78 81 85 84 87 Weight,grams 45.6 45.7 45.7 45.7 45.8 45.8 45.8 45.7 45.7 45.7 C.O.R. .821 .826.808 .804 .803 .803 .805 .809 .807 .812 Riehle Compression 49 46 55 5557 57 56 54 55 52 Barrel Cold Crack No breaks — any samples CutResistance 1-2 1-2 2-4 1-2 1-2 1-2 1-2 1-2 1-2 1-2 (1 = best, 5 = worst)SPIN PROPERTIES Spin Rate (rpm) 8707 8147 10037 10220 10451 10349 100579883 9903 9568 Launch Angle 32.10 32.96 30.51 30.19 29.93 30.07 30.3830.77 30.77 31.16 ¹Surlyn White MB (master batch) is comprised of 74.9%Surlyn ® 8528, 23.7% Unitane 0-110, .24% Ultra Blue, 1.05% Unitex O.B.and .03% Santonox R. ²Escor (Iotek) White MB (Master Batch) is comprisedof 74.9% Iotek 4000, 23.7% Unitane 0-110, .24% Ultra Blue, 1.05% UnitexO.B., and .03% Santonox R.

TABLE 6 Formulations 11 12 13 14 15 16 17 18 19 20 21 22 23 INGREDIENTSSurlyn 9910 486 486 486 486 486 — — — — — — — — Surlyn 8940 108 108 108108 108 — — — — — — — — Surlyn 8269 832 — 832 — 416 — — — — — — — —Surlyn 8265 362 362 — — 181 — — — — — — — — Surlyn 8270³ — 832 362 1194597 — — — — — — — — TG White MB¹ 193 193 193 193 193 — — — — — — — —Escor 4000 — — — — — — 857 554 454 354 554 454 354 (Iotek 4000) Escor900 — — — — — 857 — 554 454 354 554 454 354 (Iotek 8000) Escor White MB²— — — — — 193 193 193 193 193 193 193 193 LDX-218 — — — — — 950 950 700900 1100 — — — (Iotek 7520) LDX-219 — — — — — — — — — — 700 900 1100(Iotek 7520) PROPERTIES Weight, grams 45.5 45.5 45.5 45.5 45.4 45.6 45.645.6 45.6 45.6 45.6 45.6 45.6 Riehle Compression 53 57 55 59 57 56 57 5254 56 52 54 57 C.O.R. .807 .804 .808 .802 .806 .807 .800 .811 .807 .803.810 .805 .802 Shore C Hardness 88 88 87 86 87 88 86 90 87 84 88 86 85Cut Resistance 2-4 2-3 2-4 2-4 2-3 2-4 3-4 2-3 2-4 2-4 2-4 2-4 2-4¹Surlyn White MB (master batch) is comprised of 74.9% Surlyn ® 8528,23.7% Unitane 0-110, .24% Ultra Blue, 1.05% Unitex O.B. and 0.03%Santonox R. ²Escor (Iotek) White MB (Master Batch) is comprised of 74.9%Iotek 4000, 23.7% Unitane 0-110, .24% Ultra Blue, 1.05% Unitex O.B., and.03% Santonox R. ³Surlyn ® 8270 is a low modulus, zinc neutralizedpoly(ethylene-methacrylic acid-butyl acrylate) ionomer similar incomposition and properties to the sodium neutralized Surlyn ® 8265 and8269 soft ionomers.

TABLE 7 Formulations 24 25 26 27 28 29 30 31 32 33 INGREDIENTS Iotek7030 (4000) — 22.6 20.3 17.7 22.6 20.2 17.7 20.2 17.7 15.2 Iotek 8000(900) — 22.6 20.2 17.7 22.6 20.2 17.7 20.2 17.7 15.2 Iotek 7510 — — — —45.0 50. 55. 25. 27.5 30.0 Iotek 7520 — 45.2 50. 55. — — — 25. 27.5 30.Iotek White MB — 9.6 9.6 9.6 9.6 9.6 9.6 9.6 9.6 9.6 Surlyn 8269 49.1 —— — — — — — — — Surlyn 8265 21.4 — — — — — — — — — Surlyn 9910 15.2 — —— — — — — — — Surlyn 8940 4.7 — — — — — — — — — Surlyn White MB 9.6 — —— — — — — — — PROPERTIES Weight, grams 45.6 45.6 45.3 45.6 45.6 45.745.7 45.7 45.7 45.8 Riehle Compression 56 56 56 55 55 56 57 55 56 56C.O.R. .809 .810 .810 .810 .812 .811 .809 .811 .809 .809 Shore D 55 5756 55 58 57 56 57 54 54 Spin Rate (rpm) 10,328 10,061 10,193 10,33510,087 10,220 10,246 10,243 10,273 10,317 Spin Rate (rpm) ofproduction/commercial samples tested with above: Titleist Tour 100 9,489Tour Edition 100 10,152 Tour Edition 90 9,897 TF Plus II 6,803

DISCUSSION OF THE EXAMPLES

The above examples indicate that the use of the new acrylic acid basedsoft ionomers (i.e. the Iotek 7520 and the Iotek 7510 resins) incombination with relatively hard ionomers (i.e. Surlyn® 9910 and 8940,more preferably, Iotek 4000 or 8000) produce golf balls exhibitinghigher C.O.R. values (i.e. thus better distance) while maintaining, andin many instances improving, the softness and playabilitycharacteristics of the balls when compared to golf balls produced withthe methyacrylic acid based soft ionomers (i.e. Surlyn® 8265 and 8269)currently used in the Tour Edition® ball. In addition, the examplesindicate that the improvements in softness and/or distance propertiesare produced without the expense of the cover composition's overalldurability. As a result, the new ionomer cover formulations of thepresent invention produce golf balls which are longer in distance andsofter than any other prior Spalding golf ball.

More particularly, Examples 1-2 represent golf ball cover compositionsproduced utilizing only hard ionomers. While these cover compositionsproduce golf balls exhibiting high C.O.R. (i.e. greater than 0.820)values, these balls are too hard to offer sufficient playability (ShoreC Hardness greater than 90, and Riehle Compression less than 50)

Examples 3, 11-15 and 24 represent the hard-soft ionomer cover blendswhich are the subject of U.S. Pat. No. 4,884,814, and are essentiallyequivalent to the current Tour Edition® ball. Examples 12-15 varydepending on the type of methacrylic acid based soft Surlyn® ionomerutilized.

Examples 6-10 and 16-23 represent the hard-soft ionomer blends of thepresent invention. When compared to the prior art golf balls (i.e.Examples 3 and Examples 11-15), these golf balls have higher C.O.R.values, while exhibiting improved playability 35 characteristics. Thisis particularly demonstrated in Examples 19 and 22, the preferredembodiments of the present invention, which are representative of thechemical composition of the new Tour Edition® ball (i.e. the TourEdition® 90 ball) soon to be introduced into the marketplace.

In addition, the data set forth in the Examples also indicate that thehard acrylic acid based ionomeric resins (i.e. Iotek 4000 and 8000),which are sodium or zinc salts of poly(ethylene acrylic acid), produce,when utilized with the new acrylic acid based soft ionomers of thepresent invention, cover compositions exhibiting enhanced C.O.R. values(thus, improved travel distance) at the same or similar hardness whencompared with hard methyacrylic acid based ionomeric resins (i.e.Surlyn® 9910 and 8940) which are sodium or zinc salts of poly(ethylenemethacrylic acid). This can be seen in comparing Examples 6-10 withExamples 4 and 5. Thus, the more preferred compositions of the presentinvention comprise hard-soft ionomer blends comprised of acrylic acidbased hard ionomeric resins with the acrylic acid based soft ionomericresins.

Furthermore, the data set forth in Table 7 indicates that slightimprovements in C.O.R. values is produced when Iotek 7510 is substitutedfor Iotek 7520 (i.e. see Examples 28 and 29 in comparison to Examples 25and 26). Moreover, the data demonstrates that use of Iotek 7510 aloneand/or in combination with Iotek 7520 produces, when used in conjunctionwith hard ionomers, golf ball covers exhibiting higher C.O.R. values atsimilar hardness than those produced by known hard-soft ionomer blends.

In addition, because the new acrylic acid based soft ionomeric resinsavailable from Exxon under the Iotek designation (i.e. Iotek 7520 andIotek 7510) contain no wax or other processing additives (i.e. it isbelieved that Surlyn® 8265 and 8269 use 0.5-1 wt.% of a bis-stearamidewax to prevent clumping and mixing during processing), fairlysubstantial cost savings can be produced due to the potentialelimination of epoxy primer, thereby reducing volatile emissions andimproving whiteness. Moreover, use of the acrylic acid based soft Iotekionomer resin offers a significant cost savings over the softmethacrylic acid based Surlyn® ionomers not only in the overall cost perpound, but also because the new acrylic acid based soft ionomers aresubstantially softer than the methacrylic acid based Surlyn® blends,lower levels can be utilized.

In addition to the above indicated test results, the distance andplayability properties of the more preferred formulations of the presentinvention (i.e. Examples 19 and 22, which are representative of thechemical composition of Spalding's new, longer distance and slightlysofter, Tour Edition® 90 golf ball) were compared with variouscombinations of Spalding's current Tour Edition® (TE), Tour Edition® 100(TE 100), and Top Flight® II (TF II) golf balls, as well as a number ofcompetitive golf balls, and the following performance results wereproduced.

TABLE 8 DISTANCE TEST Club: 90 Deg. Metal Wood Driver   Club Head Speed(fps) 160 Launch Conditions Before Test After Test Launch Angle 8.3 N/ABall Speed (fps) 239 N/A Spin Rate (rpm) 3232 N/A Turf Conditions FirmFirm and Dry Wind 1 mph 3 mph Temperature N/A 90 Relative Humidity N/AN/A TEST RESULTS BALL TYPE TRAJ. FT. CARRY DIFF. DEV. ROLL. TOTAL DIFF.TFII 13.1 6.4 254.8  0.0 0.6 18.5 273.3  0.0 TE 100 14.4 6.8 251.6 −3.22.0 15.5 267.2 −6.2 TE 90 12.8 6.5 251.6 −3.2 1.0 19.6 271.2 −2.1TITLEIST BALATA 12.7 6.6 245.2 −9.6 4.5 21.0 266.4 −6.9 TITLEIST DT 12.96.6 250.0 −4.8 2.4 18.5 268.5 −4.8 MAXFLI ST 17.1 6.8 247.0 −7.8 −0.3 12.9 260.0 −13.4  MAXFLI BALATA 13.1 6.6 246.3 −8.5 1.7 19.9 266.2 −7.2PRECEPT BALATA 15.4 6.8 247.3 −7.5 2.0 16.4 263.7 −9.6

TABLE 9 DISTANCE TEST Club: 5 iron   Club Head Speed (fps) 125 LaunchConditions Before Test After Test Launch Angle (deg.) N/A N/A Ball Speed(fps) N/A N/A Spin Rate (rpm) N/A N/A Turf Cond. Firm Firm Wind 4 mph 7mph Temperature N/A N/A Relative Humidity N/A N/A TEST RESULTS BALL TYPETRAJ. FT. CARRY DIFF. DEV. ROLL. TOTAL DIFF. TFII 24.1 6.0 177.8  0.02.1 17.3 195.1 −0.1 TE 100 23.1 5.9 173.9 −3.9 1.8 18.8 192.8 −2.4 TE 9022.5 5.9 176.4 −1.4 2.8 18.8 195.3  0.0 TITLEIST BALATA 22.6 5.8 173.7−4.1 4.4 21.0 194.6 −0.6 TITLEIST DT 22.5 5.9 176.6 −1.2 2.3 16.9 193.5−1.7 MAXFLI ST 23.8 5.9 172.0 −5.8 2.5 19.4 191.4 −3.8 MAXFLI BALATA23.9 5.8 173.5 −4.3 4.3 21.5 195.0 −0.2 PRECEPT BALATA 23.8 5.8 170.3−7.5 3.6 20.8 191.1 −4.1

Comments: Statistical analysis of the results shows that for TE 90 vs.(4) of the competitive brands (Titleist Balata, Maxfli St., MaxfliBalata, Balata Precept) the differences in total distance are verysignificant. This means the longer total distance is likely due todifferences in ball performance and is not due to random choice.

TABLE 10 SPIN TEST Full Standard Ball Type Square Hit¹ Deviation TourEdition 9701 550 Tour Edition 100 10181 290 Tour Edition 90 9581 630 TopFlite XL 7635 772 Titleist 384 9775 99 Tour 100 Titleist Tour 100 9830232 Titleist DT 90 7700 882 Maxfli ST 8228 735 Maxfli DDH 9276 231Bridgestone 9050 253 Precept Wilson Staff 6989 719 ¹The full (squarehit) was performed utilizing a Johnny Miller Finesse wedge with its faceoriented for a square hit.

In view of the above test results, as well as additional data producedby internal testing, the following performance profile of the morepreferred formulation of the present invention (i.e. Examples 19 and 22concerning the new softer Tour Edition® 90 golf ball) has beendeveloped:

1. In machine tests, the Tour Edition® 90 distance off the #5 iron anddriver is longer than the current Tour Edition® 100 with slightly lowertrajectory.

2. The Tour Edition® 90 is equal to the Top Flite® II in distance offthe #5 iron and although two yards shorter than the Top Flite® II of fthe driver, it is significantly longer off the driver than the topcompetitive brands.

3. Spin off a full #9 iron is equal to the Tour Editions and slightlyless than the Tour Editions 100.

4. Durability in lab testing is equal to the Tour Edition® or TourEdition® 100.

As a result, the new hard-soft ionomer blends of the present inventionproduce golf balls exhibiting properties of enhanced distance andplayability without sacrificing durability.

The invention has been described with reference to the preferredembodiment. Obviously, modifications and alterations will occur toothers upon reading and understanding the preceding detaileddescription. It is intended that the invention be construed as includingall such modifications and alterations insofar as they come within thescope of the appended claims or the equivalents thereof.

Having thus described the preferred embodiments, the invention is nowclaimed to be:
 1. A golf ball having a Coefficient of Restitution ofequal to or greater than 0.810 comprising a core and a cover, whereinsaid cover comprises: from about 90 to about 10 percent by weight of ahard ionomer which is a sodium or zinc salt of the copolymer of anolefin having from 2 to 8 carbon atoms and an unsaturated monocarboxylicacid having from 3 to 8 carbon atoms, wherein said hard ionomer has ahardness greater than 50 on the Shore D scale and a flexural modulus offrom about 15,000 to about 70,000 psi; and, from about 10 to about 90percent by weight of an acrylic acid based soft ionomer which is asodium or zinc salt of a terpolymer of ethylene, acrylic acid, andmethyl acrylate, wherein said soft ionomer has a hardness from about 30to about 40 on the Shore D scale and a flexural modulus of from about3,000 to 7,000 psi.
 2. The golf ball of claim 1, wherein the hardionomer is a copolymer of ethylene and acrylic acid.
 3. The golf ball ofclaim 1, wherein the soft ionomer is a zinc salt of a terpolymer ofethylene, acrylic acid and methyl acrylate.
 4. The golf ball of claim 1,wherein the soft ionomer is a zinc salt of a terpolymer of ethylene,acrylic acid and methyl acrylate and wherein about 40 percent to about60 percent of the carboxylic acid groups of the acrylic acid areneutralized by zinc ions.
 5. The golf ball of claim 1, wherein saidcover composition comprises from about 70 to about 30 percent by weightof the hard ionomer and from about 30 to about 70 by weight percent ofthe soft ionomer.
 6. The golf ball of claim 1, wherein said covercomposition comprises from about 60 to about 40 percent by weight of thehard ionomer and from about 40 to about 60 percent by weight of the softionomer.
 7. The golf ball of claim 1, wherein said cover comprises amixture of one or more pigments, an optical brighteners and/or dye.